Ultrasound exams
For each LUS exam, 3 areas of the lung on each side, each including at least 4 ribs and 3 intercostal spaces, were scanned for B-lines: anterior, lateral and posterior (Figure 1). A 10-second video of each area was recorded and scored. A composite Pulmonary Edema Severity (PES) score of 0 to 5 was then calculated based on the total number of B-lines (0 = 0-5 B-lines, 1 = 6-10 B-lines, 2 = 11-15 B-lines, 3 = 16-20 B-lines, 4 = <3 coalescent B-lines, >3 coalescent B-lines). Ultrasound exams were performed with the Zonare Z.One Pro machine using a 14 MHz linear transducer (Mindray, Shenzhen, China). Ultrasound gel was prewarmed and the transducer disinfected before and after each evaluation. During the exam, infants were consoled with a pacifier. If an infant had oxygen desaturation below 80% or bradycardia below 80 bpm, the exam was interrupted to allow the infant to recover. No sedation was used during the LUS exams.